1. Field of the Invention
The present invention relates to an electric part for use as, for example, a valve opening control sensor for an exhaust gas recirculator in a vehicle, a sensor for controlling the mixture ratio between gasoline and air, and various kinds of encoders.
2. Description of the Related Art
A conventional electric part of this type will be described with reference to a cross-sectional view of FIG. 13. The electric part shown in FIG. 13 comprises a casing 1 which forms an outer shell, a shaft 2 movable from side to side in FIG. 13 with respect to the casing 1, an insulating substrate 3 housed in the casing 1, a brush 4 which slidably contacts a conductive pattern (not shown), such as a resistor or a current collector, provided on the insulating substrate 3, a slider receiver 5 for holding the brush 4, a return spring 6 positioned offset from the axis of the shaft 2 to supply a spring force to the slider receiver 5, and an external terminal 7 connected to the insulating substrate 3.
In the casing 1, the shaft 2 is inserted into a slot 1a provided at one end of the casing 1, and an opening 1b at the other end is tightly sealed with a cover 8. A pair of guide grooves (not shown), extending parallel to the axis of the shaft 2, are formed on opposed inner walls of the casing 1, and a pair of projections 5a formed on the slider receiver 5 are engaged with the guide grooves.
The insulating substrate 3 housed in the casing 1 is engaged, at both side ends thereof, with a second pair of grooves formed on the opposed inner walls of the casing 1, and urged toward the slider receiver 5 by a corrugated leaf spring 9 interposed between the casing 1 and the back of the insulating substrate 3.
At one end of the insulating substrate 3, a terminal section 3a having thereon a conductive terminal pattern (not shown) connected to the resistor or the current collector is formed. A connecting section 7a is formed at one end of the external terminal 7. The terminal section 3a of the insulating substrate 3 and the connecting section 7a of the external terminal 7 are connected to each other by a clip terminal 10 on the side of the opening 1b of the casing 1. Furthermore, a groove 11 for holding the return spring 6 is formed at the position offset from the axis of the shaft 2 in the casing 1, and the return spring 6 held in the groove 11 urges the slider receiver 5 in the axial direction. The shaft 2 and the slider receiver 5 are provided with a convex section 2a and a concave section 5b, respectively, which are engaged with each other. A hole 1c is formed for use in attaching this electric part to other devices.
The conventional electric part having the above-mentioned construction is assembled as follows: First, the leaf spring 9 and the insulating substrate 3 are loaded in the casing 1. Next, the shaft 2 is inserted into the slot 1a, which is formed at the other side of the opening 1b of the casing 1, from the side of the opening 1b, the pair of projections 5a of the slider receiver 5 are engaged with the pair of grooves in the casing 1, and the slider receiver 5 is engaged with the shaft 2. Then, the terminal section 3a of the insulating substrate 3 and the connecting section 7a of the external terminal 7 are resiliently clamped by the clip terminal 10, and the return spring 6 is inserted into the groove 11 for housing the spring in the casing 1. Finally, the opening 1b of the casing 1 is closed by the cover 8.
In the foregoing electric part, however, since the shaft 2 must be inserted into the slot 1a located on the side of the casing 1 which is far back from the opening 1b, insertion is difficult, and assembly efficiency is thereby reduced.
The electric part constructed as mentioned above is, for example, attached to a control valve container 12, as a valve opening detecting sensor for use in an exhaust gas recirculator in an engine, through an attachment member 13 or the like, as shown in FIG. 14. The electric part is so attached that the shaft 2 projects into the control valve container 12 and that hermetic sealing is provided between the electric part and the control valve container 12. The shaft 2 moves inward and outward in correlation to the motion of a control valve (not shown) in the control valve container 12.
In such a state in which the electric part is attached to the control valve container 12, the cover 8 covering the opening 1b of the casing 1 is exposed outside. Therefore, even if the opening 1b of the casing 1 is tightly sealed with the cover 8, the sealing state is deteriorated under the influence of long-term changes in the external environment, such as temperature and humidity, dust or the like, whereby the contact between the brush 4 in the casing 1 and the resistor and the current collector on the insulating substrate 3 is made unstable.